I found the same issue with M2, I'm in the early troll cave as a Dwarven Priest and regardless of who I attack, only that troll aggros, the rest just stand there like I'm friendly, even if they run right trough someone, it doesn't aggro them.
(Not sure if I should repost in M2, or not)
However, I must note that aggroing seemed to work properly when an early level undead priest with the scarlet crusaders that are in the starting area, so it might just be "Yellow" mobs (the ones that don't aggro purely based on location).